This invention relates to a tuning apparatus for use in a television apparatus, and more particularly, to a tuning apparatus for the VHF band of the television receiver.
Generally, television receivers have mechanical tuners or electronic synchronous tuners, which are used as a tuner for VHF (Very-High Frequency) band and a tuner for UHF (Ultra-High Frequency) band. Each of these tuners comprises an input tuning circuit, a high-frequency amplifier circuit, a mixer for providing intermediate-frequency television signals, and a local oscillating circuit.
An electronic synchronous tuner needs to be switched for a low band (e.g., 90 to 108 MHz) or a high band (e.g., 170 to 222 MHz), in accordance with the frequency of the television signals. Hence, in order to prevent undesired signal-mixing, a band trap circuit is provided within the input tuning circuit of the tuner. The band trap circuit functions as a high-band trap while the television receiver is receiving low-band television signals, and as a low-band trap while the television receiver is receiving high-band television signals.
Recently, there has been a demand for tuners which can receive cable television (CATV) signals. The frequency of the CATV signals is high. It is therefore necessary for the band trap circuit of such a tuner to receive low-band signals whose frequency range is broader and also high-band signals whose frequency range is broader. The band trap circuit of the type used in the electronic synchronous tuner designed for the ordinary television receivers cannot trap all signals of unnecessary frequencies. Hence, there has been an increasing demand that the tuners be improved, thereby to receive CATV signals as well as ordinary television signals.